THE   UNIVERSITY 

OF  ILLINOIS 

LIBRARY 


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AGRICULTURAL 

LIBRARY 


BULLETIN  No    199 


GERM  CONTENT  OF  MILK 

I.    AS  INFLUENCED  BY  THE  FACTORS  AT  THE  BARN 


BY  M.  J.  PEUCHA  AND  H.  M.  WEETEK 


URBANA,  ILLINOIS,  MAY,  1917 


CONTENTS  OP  BULLETIN  No.  199 

PAGE 

1.  FOREWORD 23 

2.  INTRODUCTION 25 

3.  THE  THREE  BARNS  IN  WHICH  THE  STUDY  WAS  MADE 26 

4.  METHODS  OF  STUDY 30 

5.  EESULTS  OF  THE  STUDY 32 

Germ  Content  of  the  Individual  Samples  of  Milk 40 

Average  Germ  Content  of  the  Milk  of  the  Different  Animals   41 

Average  Germ  Content  of  All  the  Milk  at  Different  Milkings 43 

Comparison  of  the  Results  for  1914  and  for  1915 46 

Number  of  Bacteria  Added  to  the  Milk  by  All  the  Barn  Factors  in  Each 
of  the  Three  Barns 43 

6.  SUMMARY 51 

7.  CONCLUSIONS  .  .  .51 


FOREWORD 

The  public  desire  and  should  be  able  to  obtain  a  supply  of  satis- 
factorily clean  and  wholesome  milk.  The  representatives  of  the  con- 
suming public  in  this  matter,  the  health  officials,  have  frequently 
adopted  the  germ  content  of  milk  as  an  index  of  cleanliness  and  whole- 
someness.  In  this  way,  the  legal  limit  of  germ  life  permissible  in  the 
milk  supply  as  shown  by  the  plate  count  has  been  placed  in  Champaign- 
Urbana  at  100,000  per  cubic  centimeter  and  in  St.  Louis  at  5,000,000 
per  cubic  centimeter. 

No  matter  what  is  our  personal  judgment  regarding  the  wisdom 
of  such  bacterial  standards,  the  legally  constituted  authorities  having 
thus  established  these  limits  of  bacterial  content,  the  burden  rests  upon 
the  producer  and  the  retailer  to  observe  them.  When  adjusting  their 
business  methods  to  such  variable  limits  as  those  mentioned  above, 
it  is  important  that  the  dairymen  have  fairly  accurate  knowledge  of 
the  relative  importance  of  the  various  dairy  operations  upon  the 
germ  content  of  the  milk. 

In  the  general  directions  which  the  health  officials  have  formulated 
for  the  guidance  of  the  dairymen,  great  stress  has  been  laid  upon  the 
construction  and  condition  of  the  cow  stable.  Accordingly,  technical 
studies  of  the  influence  of  dairy  factors  naturally  included  a  measure- 
ment of  the  influence  of  barn  conditions.  The  results  obtained  at  the 
New  York  Agricultural  Experiment  Station  from  such  technical 
studies  of  the  influence  of  barn  conditions  were  so  out  of  keeping  with 
the  ideas  of  the  health  officials  that  it  seemed  best  to  redetermine  inde- 
pendently this  relationship  at  this  experiment  station. 

The  surprisingly  accordant  results  which  have  been  obtained  at 
these  two  experiment  stations  should  not  be  understood  as  counte- 
nancing dirty  methods  or  dirty  milk.  They  merely  point  out  that 
earlier  impressions,  formed  in  the  absence  of  exact  data,  did  not  give 
a  correct  value  to  the  importance  of  barn  conditions  in  connection  with 
germs  in  milk. 

Neither  should  these  results  be  taken  as  a  criticism  of  health 
officials.  Such'  officers  are  charged  with  the  protection  of  the  public 
health.  Where  the  facts  are  available,  they  utilize  them.  Where 
exact  information  is  lacking,  they  must  proceed  in  accordance  with 
their  best  judgment  even  tho  they  recognize  the  fallibility  of  such 
judgment. 

The  slight  effect  of  barn  conditions  upon  the  number  of  germs 
in  milk  was  clearly  brought  out  by  the  extended  studies  at  the  New 

23 


York  Agricultural  Experiment  Station.  The  studies  here  reported 
were  made  in  a  different  part  of  the  country,  in  three  quite  dissimilar 
barns,  by  a  different  laboratory  force,  using  a  different  method  of 
attacking  the  problem.  The  results  of  this  latter  study  are  quite  in 
accord  with  those  obtained  in  New  York. 

The  earlier  misconceptions  of  health  officials  regarding  the  im- 
portance of  barn  conditions  resulted  in  placing  unjust  economic  bur- 
dens upon  the  producer.  Now  that  more  accurate  data  upon  this 
question  is  available  it  is  to  be  hoped  that  these  burdens  will  be  more 
fairly  distributed. 

H.  A.  HARDING 
Chief  in  Dairy  Husbandry 


24 


GERM  CONTENT  OF  MILK 

I.  AS  INFLUENCED  BY  THE  FACTORS  AT  THE  BARN 

By  M.  J.  PEUCHA,  ASSISTANT  CHIEF  IN  DAIRY  BACTERIOLOGY,  and 
H.  M.  WEETER,  ASSISTANT  IN  DAIRY  HUSBANDRY 


The  studies  on  which  this  bulletin  is  based  are  a  part  of  an  investi- 
gation begun  by  H.  A.  Harding  in  1906  at  the  New  York  (Geneva) 
Agricultural  Experiment  Station.  In  an  introduction  to  Bulletin  365 
of  that  institution  Dr.  Harding  makes  the  following  statement  as  to 
the  purpose  of  the  investigation:  "When  health  officials,  failing  to 
find  other  means  of  characterizing  sanitary  milk,  undertook  to  specify 
the  conditions  under  which  it  should  be  produced,  they  were  confronted 
by  an  almost  total  lack  of  detailed  information  upon  this  subject.  This 
lack  arose  from  the  fact  that  available  studies  upon  milk  sanitation 
were  in  the  nature  of  general  surveys  of  the  situation.  While  these 
general  surveys  were  a  necessary  preliminary,  they  gave  little  informa- 
tion as  to  either  the  absolute  or  the  relative  importance  of  any  given 

dairy  operation The  importance  of  the  interests  involved 

demands  that  the  needed  information  shall  be  furnished  as  promptly 
as  possible." 

Investigations  toward  this  end  have  been  carried  on  at  the  New 
York  Agricultural  Experiment  Station  since  1906. 1  The  aim  in  these 
investigations  has  been  to  separate  the  various  sources  of  contamina- 
tion to  which  milk  is  subject  and  to  measure  the  influence  of  each  on 
the  germ  content  of  milk.  The  results  from  these  studies  point  to  the 
conclusion  that  barn  conditions  and  barn  operations  have  only  a  small 
influence  upon  the  germ  content  of  milk. 

If  the  above  conclusion  is  true,  it  will  radically  change  our  con- 
ception concerning  the  relative  importance  of  the  different  sources  of 
milk  contamination.  Since  it  is  an  axiom  in  scientific  work  that  no 
important  results  are  accepted  until  they  have  been  verified  independ- 

^Harding,  H.  A.,  Wilson,  J.  K.,  and  Smith,  G.  A.  Milking  Machine:  Effect  of 
Methods  of  Handling  on  the  Germ  Content  of  Milk.  N.  Y.  (Geneva)  Agr.  Exp. 
Sta.  Bui.  317.  1909. 

Harding,  H.  A.,  and  Wilson,  J.  K.  The  Modern  Milk  Pail.  N.  Y.  (Geneva) 
Agr.  Exp.  Sta.  Bui.  326,  pp.  248-281.  1910. 

Harding,  H.  A.,  Ruehle,  G.  L.,  Wilson,  J.  K.,  and  Smith,  G.  A.  The  Effect  of 
Certain  Dairy  Operations  upon  the  Germ  Content  of  Milk.  N.  Y.  (Geneva)  Agr. 
Exp.  Sta.  Bui.  365,  pp.  198-233.  1913. 

Harding,  H.  A.,  and  Wilson,  J.  K.  A  Study  of  the  Udder  Flora  of  Cows. 
N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Tech.  Bui.  27.  1913. 

Buehle,  G.  L.  A.,  and  Kulp,  W.  L.  Germ  Content  of  Stable  Air  and  Its  Effect 
upon  the  Germ  Content  of  Milk.  N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Bui.  409,  pp. 
418-474.  1915. 

25 


26  BULLETIN  No.  199 

ently  by  other  workers,  it  was  decided  to  repeat  the  study  made  at 
the  New  York  Station  upon  the  influence  of  barn  conditions  and  oper- 
ations on  the  germ  content  of  milk.  Accordingly,  the  subject  has  been 
restudied  at  the  Illinois  Station  by  a  new  force  of  workers,  in  a  new 
laboratory,  and  in  three  barns  of  distinctly  different  types.  The 
method  of  attack  in  the  present  study  differed  from  the  method  used 
at  the  New  York  Station  in  that  all  the  barn  factors  were  grouped 
together  and  their  collective  influence  on  the  germ  content  of  the  milk 
was  determined.  In  these,  as  in  the  previous  studies,  the  utensils  were 
considered  as  a  separate  source  of  contamination  and  were  therefore 
thoroly  steamed  before  each  milking.1 

THE  THREE  BARNS  IN  WHICH  THE  STUDY  WAS  MADE  AND 
THE  DAIRY  METHODS  EMPLOYED  IN  EACH 

In  order  that  the  results  of  this  study  may  be  thoroly  understood 
and  their  significance  fully  appreciated,  it  is  necessary  to  give  a  some- 
what full  description  of  the  conditions  and  the  dairy  operations  in 
each  of  the  three  barns  in  which  the  experiment  was  conducted. 

Barn  I  is  a  two-story  frame  building  75  feet  long  and  45  feet  wide. 
There  are  approximately  900  cubic  feet  of  space  and  9  square  feet  of 
window  glass  per  cow.  Two  rows  of  iron  stalls  facing  the  central 
aisle  and  running  lengthwise  accommodate  forty  cows.  The  length  of 
the  floor  from  the  manger  to  the  gutter  is  5  feet  5  inches  in  one  row 
of  stalls  and  5  feet  in  the  other  row.  The  iron  stalls  used  in  this  barn 
are  known  as  ' '  Drown ' '  stalls,  and  are  so  constructed  that  it  is  possible, 
to  a  certain  extent,  to  adjust  the  space  inside  the  stall  to  the  size  of  the 
animal. 

The  ceiling  and  the  walls  are  constructed  of  matched  lumber,  are 
painted,  and  are  without  any  large  crevices.  The  floor,  the  gutters, 
and  the  mangers  are  of  cement.  The  feeding  materials  are  stored  in  a 
separate  part  of  the  building  and  are  brought  into  the  barn  thru  an 
end  door. 

During  the  investigation,  the  milkings  began  at  five  in  the  morn- 
ing and  at  four  in  the  afternoon  and  lasted  an  hour  and  a  half.  After 
the  morning  milking,  the  cows  were  turned  out  into  a  yard,  the  manure 
was  taken  out,  the  floors  were  flushed  with  water,  and  the  stalls  were 
bedded  with  sawdust.  When  feasible,  the  manure  was  placed  directly 
on  the  wagon  and  taken  away.  At  other  times  it  was  dumped  about 
thirty-five  feet  from  the  barn  in  a  yard  to  which  the  cows  did  not  have 
access.  A  tight  board  fence,  six  feet  high,  separated  this  manure  pile 
from  the  barn. 

After  the  barn  had  been  cleaned,  the  cows  were  brought  back,  fed 
hay,  and  cleaned.  The  amount  of  time  spent  on  the  cleaning  of  the 

irThe  influence  of  dairy  utensils  upon  the  germ  content  of  milk  has  been  studied 
separately  and  the  results  will  be  reported  later. 


1917} 


GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  BARN  FACTORS 


27 


cows  was  approximately  five  minutes  to  each  animal.  Occasionally 
the  cows  were  used  for  demonstration  purposes  before  classes,  and  for 
such  occasions  their  udders  and  flanks  were  clipped.  This  clipping, 
however,  was  not  practiced  regularly  for  the  purpose  of  reducing  the 
number  of  bacteria  in  the  milk.  Likewise,  during  the  experiment,  no 
systematic  attempt  was  made  to  clean  the  cows  before  each  milking. 
If  any  of  them  became  dirty  prior  to  the  milking,  the  milker  wiped 
the  loose  dirt  from  their  flanks  and  udders  with  a  handful  of  the  saw- 
dust bedding.  In  1914  the  udders  of  the  cows  were  wiped  with  a  damp 
cloth  previous  to  the  milkings,  but  in  1915  this  practice  was  discon- 
tinued intentionally. 

During  the  milking  the  cows  were  fed  silage  and  grain.  The  hay 
was  brought  into  the  barn  usually  before  the  milking  was  finished, 
and  was  distributed  into  the  mangers.  This  operation  frequently 
caused  a  considerable  amount  of  dust  in  the  air.  The  milkers  wore 
milking  suits  which  were  changed  twice  each  week. 

Barn  II  is  a  two-story,  circular  building  70  feet  in  diameter.  There 
are  about  800  cubic  feet  of  space  and  9  square  feet  of  window  glass  per 
animal.  The  platform  upon  which  the  cows  are  stanchioned  is  circular, 
running  around  a  central  ring  45  feet  in  diameter.  Around  the  outer 
edge  of  this  platform  is  the  gutter,  and  between  the  gutter  and  the 
outside  brick  wall  runs  a  passageway  about  six  feet  in  width. 

Especial  effort  was  made  in  constructing  this  barn  to  so  equip  it 
that  the  cows  would  be  prevented  from  lying  down  in  their  own  feces. 


FIG.  1. — THE  INTERIOR  OF  DAIRY  BARN  I 


28  BULLETIN  No.  199  [May, 

This  was  accomplished  by  varying  the  width  of  the  platform  upon 
which  the  cows  are  stanchioned  and  by  installing  adjustable  stanchions. 
By  these  two  means  the  space  for  each  cow  can  be  adjusted  as  desired. 

The  brick  wall  and  the  wooden  ceiling  are  free  from  any  large 
crevices,  but  are  rough  and  not  painted.  The  platform  upon  which 
the  cows  are  stanchioned  is  paved  half  way  around  with  cork  bricks 
and  the  other  half  with  creosote  blocks.  In  the  center  of  the  barn  is  a 
silo  16  feet  in  diameter  and  the  chutes  for  the  grain  and  the  hay  which 
are  stored  on  the  second  floor. 

With  few  exceptions  the  daily  operations  in  this  barn  were  about 
the  same  as  in  Barn  I.  The  floor  was  cleaned  regularly,  but  as  a  rule 
was  not  flushed  with  water.  In  cleaning  the  cows,  only  about  one 
minute  of  labor  a  day  was  allowed  for  each  animal,  while  in  Barn  I 
a  period  of  five  minutes  was  devoted  to  that  purpose.  This  reduction 
in  labor  in  keeping  the  cows  clean  was  brought  about  by  carefully 
adjusting  to  their  size  the  spaces  in  which  the  cows  were  stanchioned. 
During  milking  and  feeding  and  in  unfavorable  weather  the  cows  were 
stanchioned  in  the  barn ;  at  other  times  they  were  turned  out  into  an 
acre  dry-lot  adjacent  to  the  barn. 

Barn  III  is  a  two-story,  round,  basement  barn  50  feet  in  diameter. 
Only  ten  cows  occupied  it  during  this  experiment,  each  animal  having 
approximately  1,500  cubic  feet  of  space  and  15  square  feet  of  window 
glass.  In  the  center  of  the  barn  are  the  silo  and  the  grain  and  the 
hay  chutes.  Around  these  is  a  circular  passageway  10  feet  in  width. 
On  the  outer  edge  of  this  passageway  are  the  mangers  and  the  stan- 
chions, both  constructed  of  wood.  There  is  only  a  dirt  floor  and  there 
are  no  gutters.  The  brick  side-walls  and  the  wooden  ceiling  are  tight 
but  are  not  painted.  During  the  experiment  the  cobwebs  and  the 
dust  were  abundant,  not  having  been  cleaned  from  the  ceiling  for 
four  years  previous. 

The  cows  were  stanchioned  only  during  the  milkings.  Between 
milkings  they  were  allowed  to  roam  about  in  the  barn  and  in  the 
quarter-acre  dry-lot  adjacent  to  the  barn.  A  large  door  leading  from 
the  barn  into  the  dry-lot  was  always  open.  The  floor  in  the  barn  was 
covered  with  straw  once  a  day,  but  the  manure  was  allowed  to  accumu- 
late on  the  floor  and  was  removed  from  the  barn  only  twice  a  year. 
The  cows  were  not  kept  as  clean  as  in  Barns  I  and  II,  but  no  manure 
was  allowed  to  accumulate  and  to  cake  on  their  flanks  and  udders. 

These  three  barns  in  a  general  way  represent  three  classes  of  dairy 
barns,  Barn  I  being  in  excellent  condition,  Barn  II  being  good,  and 
Barn  III  poor.  The  difference  between  Barn  I  and  Barn  II  as  to 
cleanliness,  however,  was  not  very  great.  On  the  other  hand,  Barn  III 
would  be  classed  as  a  dirty  barn,  and  it  is  doubtful  whether  the  milk 
from  it  would  be  admitted  to  the  market  of  some  cities.  A  photograph 
of  each  of  the  three  barns  is  shown  in  Figs.  1,  2,  and  3. 


1917]  GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  BARN  FACTORS 


29 


FIG.  2. — THE  INTERIOR  OF  DAIRY  BARN  II 


FIG.  3. — THE  INTERIOR  OF  DAIRY  BARN  III 


30  BULLETIN  No.  199 

METHODS  OF  STUDY 

Sterilization. — The  media  used  in  determining  the  germ  content 
of  the  samples  of  milk  were  sterilized  in  test  tubes  in  the  autoclave  for 
fifteen  minutes  at  120°  C.  In  order  that  all  the  test  tubes  might  receive 
the  same  amount  of  heat,  they  were  held  during  the  process  of  steriliza- 
tion in  test-tube  racks. 

All  the  glassware  and  other  laboratory  apparatus  withstanding 
dry  heat  were  sterilized  by  subjecting  them  to  160°  C.  in  a  dry  sterilizer 
for  two  hours  or  more. 

The  pails  used  for  milking  in  Barn  I  were  steamed  for  three 
minutes  over  a  jet.  In  Barns  II  and  III  the  pails  were  steamed  in  a 
sterilizer,  which  was  a  box  constructed  of  galvanized  iron.  After  such 
steaming,  the  pails  were  always  examined  for  the  presence  of  living 
bacteria  which  might  have  survived  the  steaming.  This  examination 
consisted  of  rinsing  out  each  pail  with  500  cc.  of  sterile  water  just 
previous  to  milking  and  then  determining  the  number  of  bacteria  in 
the  rinse  water. 

The  examination  indicated  that  all  the  pails  steamed  in  the  steril- 
izer and  112  of  the  130  pails  steamed  over  the  jet  were  free  from 
bacteria.  The  remaining  18  pails  steamed  over  the  jet  were  not  entirely 
sterile,  but  the  number  of  bacteria  found  in  them  was  extremely  small 
and  did  not  affect  measurably  the  results  of  this  study. 

Taking  of  Samples. — All  the  samples  were  taken  from  the  milk  of 
the  individual  cows  when  the  milker  .brought  it  in  pails  from  the  barn 
into  the  adjacent  milk  room.  The  milk  was  thus  exposed  to  all  the 
sources  of  contamination  in  the  barn.  After  a  thoro  stirring  with  a 
sterile  iron  spoon  fifteen  inches  long,  the  desired  amount  of  milk  was 
transferred  by  means  of  the  spoon  into  a  large  test  tube.  The  milk 
samples  were  immediately  cooled  to  about  54°  C.,  and  were  plated, 
as  a  rule,  within  one  hour. 

Dilutions  and  Plating. — Wide-mouthed,  glass-stoppered  bottles  of 
250-cc.  capacity  were  used  as  dilution  bottles.  This  type  of  bottle 
was  used  at  the  suggestion  of  Professor  W.  A.  Stocking,  Jr.,  of  Cornell 
University,  and  was  found  to  be  an  improvement  on  the  ordinary  dilu- 
tion bottle  with  a  cotton  plug.  The  bottles  were  sterilized  in  the  dry 
oven,  and  just  before  plating,  the  required  amount  of  sterile  water  was 
introduced  into  each  by ^  means  of  a  graduated  pipette. 

Two  dilutions,  1  to  10  and  1  to  100,  were  made  from  each  sample. 
For  the  first  dilution  5  cc.  of  milk  was  added  to  45  cc.  of  water,  and 
for  the  second  dilution,  1  cc.  of  milk  was  added  to  99  cc.  of  water. 
Every  bottle  was  then  shaken  violently,  receiving  30  double  shakes  in 
such  a  manner  that  with  each  single  stroke  the  bottle  passed  thru  a 
distance  of  ten  inches.  From  each  dilution  two  plates  were  seeded, 
each  one  with  1  cc.  of  the  bacterial  suspension. 


1917]  GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  BARN  FACTORS  31 

It  is  well  known  that  in  the  quantitative  bacteriological  examina- 
tion of  milk  by  the  plate  method,  plates  seeded  with  the  same  milk  will 
rarely  develop  the  same  number  of  colonies,  even  when  the  plating 
is  done  with  care  and  accuracy.  In  order  to  ascertain  the  extent  of 
variation  due  to  the  laboratory  methods  employed  in  this  study,  ten 
experiments  were  undertaken  in  each  of  which  100  plates  were  seeded 
with  the  same  milk.  The  same  dilution  was  used  for  all  the  plates  in 
each  experiment.  The  results  from  one  of  these  experiments  are  shown 
in  Table  1. 

TABLE  1. — FREQUENCY  DISTRIBUTION  FOR  NINETY-SIX  PLATES*  MADE  FROM  THE 
SAME  BACTERIAL  SUSPENSION 


Class 

Number  of  colonies 
per  plate 

Frequency  distribution 

1 

2 
3 
4 
5 
6 

110-120 
121-130 
131-140 
141-150 
151-160 
161-170 

111 
ItH 

IHi 
IHrl 
1W1 

liH 
IHri 

1 

1 

Utl 
1111 

im    UH    111 

li«     LHl     liH 

1111 

'Four  of  the  100  plates  were  spoiled. 

The  mean  number  of  colonies  for  all  the  plates  in  this  experiment 
was  142,  while  the  lowest  count  was  110  and  the  highest  count  was 
170.  In  order  to  show  the  frequency  distribution  of  the  plates,  they 
were  divided  into  six  classes,  each  of  which  had  a  class  range  of  ten 
units.  It  will  be  seen  from  Table  1  that  of  the  96  plates  counted,  62 
fell  into  the  third  and  fourth  classes,  having  more  than  130  and  less 
than  151  colonies.  With  respect  to  variability,  it  is  important  to  note 
that  these  individual  counts  showed  very  moderate  variation.  Indeed, 
no  individual  count  deviated  as  much  as  25  percent  from  the  average. 
The  other  nine  experiments  on  this  subject  showed  approximately  the 
same  variation.  According  to  the  theory  of  statistics,  the  average  of 
the  counts  for  sets  of  four  plates  would  tend  to  be  about  half  as  variable 
as  the  counts  of  the  individual  plates.  Since,  with  but  few  exceptions, 
every  determination  in  Tables  2  to  7  was  an  average  of  four  plates  it 
seems  reasonable  to  conclude  that  the  wide  variations  in  the  germ  con- 
tent of  the  samples  shown  in  these  tables  were  due  primarily  to  varia- 
tions in  the  number  of  bacteria  actually  present  in  the  samples  of  milk 
and  not  to  inaccuracies  of  the  laboratory  methods. 

Medium. — The  following  medium  was  used  thruout  the  entire 
study. 

Agar  shreds 15  grams 

Liebig  's  meat  extract 3        " 

Witte  's  dry  peptone 10        " 

Lactose 10       " 

Distilled  water 1000  cc. 

The  reaction  of  the  medium  was  adjusted  to  1.0  percent  normal 
acid  to  phenolphthalein. 


32  BULLETIN  No.  199  [May, 

Incubation  and  Counting. — All  the  plates  were  incubated  for  five 
days  at  20°  C.,  and  for  two  days  at  37°  C.  This  length  of  time  and  the 
two  temperatures  of  incubation  were  used  in  order  to  induce  a  larger 
number  of  the  bacteria  present  in  the  milk  to  form  visible  colonies. 
According  to  Harding  and  Wilson,1  the  bacteria  that  form  colonies 
at  37°  C.  but  not  at  20°  C.  may  occasionally  be  present  in  the  freshly 
drawn  milk. 

As  stated  above,  two  dilutions  were  made  from  each  sample  of 
milk  and  two  plates  were  seeded  from  each  dilution.  All  four  plates 
from  each  sample  were  counted  regardless  of  the  number  of  bacteria 
on  them,  unless  they  showed  some  evidence  of  contamination.  In 
Tables  2  to  7,  therefore,  the  number  of  bacteria  given  for  each  sample 
of  milk  is  an  average  based  upon  four  plates. 


As  stated  before,  the  samples  were  taken  from  the  milk  of  indi- 
vidual cows.  In  Barn  I,  511  samples  were  taken  from  35  cows  in  1914, 
and  349  samples  from  37  cows  in  1915.  In  Barn  II,  360  samples  were 
taken  from  26  cows  in  1914,  and  207  samples  from  21  cows  in  1915. 
Of  the  238  samples  in  Barn  III,  161  were  taken  from  10  cows  in  1914, 
and  77  from  9  cows  in  1915.  The  data  from  the  analyses  of  these 
samples  are  given  in  Tables  2  to  7. 

^Harding,  H.  A.,  and  Wilson,  J.  K.     A  Study  of  the  Udder  Flora  of  Cows. 
N.  Y.    (Geneva)    Agr.   Exp.   Sta.  Tech.   Bui.   27.      1913. 


1917] 


GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  BARN  FACTORS 


33 


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34 


BULLETIN  No.  199 


[May. 


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1917] 


GERM  CONTENT  OP  MILK  AS  INFLUENCED  BY  BARN  FACTORS 


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36 


BULLETIN  No.  199 


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1917] 


GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  BARN  FACTORS 


37 


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38 


BULLETIN  No.  199 


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1917] 


GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  BARN  FACTORS 


39 


TABLE  6.— GERM  CONTENT  OF  INDIVIDUAL  SAMPLES  OF  MILK: 
BARN  III,  1914 


Cow  No.  .  . 

1003  |  1015 

1018 

1019 

1025 

1026  |  1031 

1032 

1033 

1034 

Sample 
No. 

Number  of  bacteria  per  cc.  of  milk 

1 

8775 

8750 

5547 

4562 

1987 

11812 

1815 

9275 

3792 

307 

2 

7725 

6705 

8125 

1925 

5675 

12325 

2166 

5625 

2980 

647 

3 

17750 

8472 

2350 

2820 

22146 

19825 

1483 

6582 

4955 

1000 

4 

9875 

1453 

2120 

865 

1923 

14175 

1088 

5260 

2090 

538 

5 

11650 

3525 

3675 

563 

970 

16600 

1110 

3275 

855 

433 

6 

25312 

3433 

5735 

7285 

2130 

13265 

1932 

6457 

1757 

652 

7 

15237 

6110 

10977 

1092 

3060 

21075 

5912 

4733 

5282 

1072 

8 

8095 

12108 

3048 

1223 

2117 

16875 

2338 

3788 

3193 

645 

9 

9725 

4202 

4977 

1962 

2045 

14725 

1510 

1870 

1825 

857 

10 

10338 

9380 

2905 

1620 

3255 

34525 

2343 

5673 

2695 

1198 

11 

29500 

4417 

2287 

3900 

18400 

2112 

2285 

4647 

892 

12 

9700 

5210 

3820 

4860 

14087 

3215 

6692 

3915 

5875 

13 

19150 

9792 

2707 

2555 

63835 

1620 

1575 

5367 

20365 

14 

5825 

2215 

5062 

4498 

9125 

2340 

4675 

3895 

3537 

15 

18950 

3505 

3300 

3552 

26135 

9690 

1390 

cjqoc; 

OQQfl 

16 

3425 



2177 

3150 

4452 

7480 

9725 

5606 

tij/ijtj 
6480 

LJtJO\J 

3000 

17 

12013 

13735 

2475 

10300 

3430 

18520 

1972 

Average 

13120 

6414 

5324 

2748 

4320 

19092 

3150 

4603 

4598 

2667 

TABLE  7. — GERM  CONTENT  OF  INDIVIDUAL  SAMPLES  OF  MILK: 
BARN  III,  1915 

Cow  No 113        137       1015      1018      1019     1031      1032      1033    |  1034 


Sample  No. 


Number  of  bacteria  per  cc.  of  milk 


1 

20800 

2347 

7270 

3197 

3787 

1252 

4355 

4515 

342 

2 

13760 

2277 

4787 

7117 

1317 

1745 

4922 

2787 

3 

2052 

2767 

5025 

7920 

5687 

6362 

2957 

2047 

4 

1315 

2300 

9877 

3967 

8377 

8690 

3120 

6467 

5 

1065 

2230 

17705 

2890 

1877 

8970 

8350 

690 

6 

905 

1175 

6672 

48600 

6252 

•  •  •  • 

9472 

4265 

1230 

7 

2350 

2257 

4235 

2395 

725 

800 

3807 

2610 

8 

4885 

1325 

4067 

1752 

2085 

6392 

1537 

9 

18602 

887 

9456 

3777 

2107 

3292 

5180 

447 

10 

4185 

3680 

4635 

6225 

1555 

Average  

6991 

2124 

9178 

9342 

3759 

4010 

5086 

4834 

1971 

40 


BULLETIN  No.  199 


[May, 


GERM  CONTENT  OF  THE  INDIVIDUAL  SAMPLES  OF  MILK 

Since  the  samples  for  this  study  were  taken  from  the  milk  of  the 
individual  cows  after  it  was  brought  in  the  pails  from  the  barn  into 
the  milk  room,  the  number  of  bacteria  present  in  the  milk  was  due  to 
the  collective  influence  of  all  the  different  sources  of  contamination  at 
the  barns.  An  examination  of  the  foregoing  tables  shows  that  nearly 
every  sample  of  milk  had  a  different  number  of  bacteria.  Among  the 
samples  from  Barn  I,  the  lowest  germ  content  was  17  and  the  highest 
was  218,250  bacteria  per  cubic  centimeter  of  milk;  in  Barn  II  the 
lowest  was  3  and  the  highest  was  33,000 ;  and  in  Barn  III  the  lowest 
was  307  and  the  highest  was  63,835.  These  are  wide  limits  of  variation 
in  the  germ  content  of  milk  produced  under  uniform  barn  conditions. 
However,  the  number  of  samples  with  high  germ  content  was  very 
small,  especially  in  Barn  II  and  Barn  I ;  as  a  matter  of  fact,  most  of 
the  samples  of  milk  had  an  extremely  low  germ  content.  This  is  a  con- 
spicuous feature  of  the  data,  which  is  brought  out  more  clearly  by 
arranging  the  samples  into  the  groups  shown  in  Table  8. 

TABLE  8. — GROUPING  OF  ALL  MILK  SAMPLES  ACCORDING  TO  GERM  CONTENT 


Between 

Between 

Between 

Below  1,000 
per  cc. 

1,000  and 
5,000 

5,000  and 
10,000 

10,000  and 
50,000 

Over  50,000 
per  cc. 

per  ce. 

per  ce. 

per  cc. 

Barn  I  

472 

297 

56 

29 

6 

Barn  II  

405 

153 

4 

5 

0 

Barn  III  

19 

127 

57 

34 

1 

Total  

896 

577 

117 

68 

7 

Of  the  860  samples  from  Barn  I,  472,  or  54.9  percent,  fall  into  the 
first  group ;  297,  or  34.5  percent,  fall  into  the  second  group ;  56,  or 
6.5  percent,  fall  into  the  third  group ;  29,  or  3.4  percent,  fall  into  the 
fourth  group ;  and  6,  or  0.7  percent,  fall  into  the  fifth  group.  In 
Barn  II,  405  samples,  or  71.4  percent,  fall  into  the  first  group ;  153,  or 
27  percent,  fall  into  the  second  group ;  4,  or  0.7  percent,  into  the  third 
group ;  5,  or  0.9  percent,  into  the  fourth  group ;  and  not  a  single  sample 
is  in  the  fifth  group.  In  Barn  III,  19  samples,  or  8  percent,  are  in  the 
first  group ;  127,  or  53.3  percent,in  the  second  group ;  57,  or  24  percent, 
in  the  third  group ;  34,  or  14.2  percent,  in  the  fourth  group ;  and  only 
one  sample,  or  0.5  percent,  in  the  fifth  group. 

The  influence  of  the  barn  conditions  upon  the  germ  content  of 
milk  from  the  individual  cows  is  clearly  seen  in  the  above  grouping  of 
the  samples.  As  judged  by  the  general  appearance  of  the  barns  and 
by  the  amount  of  labor  devoted  to  the  cleaning  both  of  the  barns  and 
of  the  cows,  Barn  I  was  cleaner  than  Barn  II,  and  Barn  III  was  the 
dirtiest  of  the  three  barns.  It  is  seen  from  the  above  data  that  the 
samples  of  milk  from  Barn  III  had,  on  the  average,  decidedly  higher 


1917]  GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  BARN  FACTORS  41 

germ  content  that  the  samples  from  Barns  I  and  II,  but  in  view 
of  the  difference  between  the  conditions  in  Barn  III  and  the  conditions 
in  the  other  two  barns  it  seems  remarkable  that  so  many  samples  from 
Barn  III  had  such  a  low  germ  content  and  that  the  difference  between 
the  results  from  this  barn  and  those  from  the  other  two  barns  was  so 
small. 

The  comparison  of  the  results  from  Barn  I  with  those  from 
Barn  II,  on  the  other  hand,  shows  that  there  was  a  larger  propor- 
tion of  the  samples  from  Barn  II  with  a  low  germ  content  than  from 
Barn  I,  in  spite  of  the  fact  that  the  latter  barn  was  cleaner.  This  and 
the  fact  that  most  of  the  samples  from  both  barns  had  such  low  germ 
content  clearly  indicate  that  the  barn  conditions  and  operations  in 
these  two  barns  contributed  but  a  small  number  of  bacteria  to  the 
milk.  Why  there  should  have  been  a  larger  number  of  samples  with 
high  germ  content  from  Barn  I  than  from  Barn  II  is  not  certain,  but  it 
will  be  noticed  that  most  of  the  samples  with  high  germ  content  in  this 
barn  came  from  certain  few  animals.  The  most  conspicuous  case  was 
Cow  55.  This  animal  persistently  gave  milk  with  high  germ  content 
and  subsequent  studies  showed  that  her  udder  was  the  source  of  these 
larger  numbers  of  bacteria  in  her  milk. 

AVERAGE  GERM  CONTENT  OF  THE  MILK  OF  THE  DIFFERENT  ANIMALS 

The  average  germ  content  of  the  milk  of  each  animal  was  calcu- 
lated from  the  data  in  Tables  2  to  7.  It  was  obtained  by  adding  the 
germ  content  of  all  the  samples  taken  from  the  animal  and  then  divid- 
ing the  sum  by  the  number  of  samples.  The  calculations  were  made 
for  1914  and  1915  separately.  With  but  few  exceptions,  each  average 
in  1914  represents  fifteen  to  seventeen  samples  and  in  1915  ten  samples. 
In  all,  samples  were  taken  from  89  different  cows,  49  of  which  were 
milked  during  both  years,  so  that  138  averages  were  obtained;  these 
are  shown  in  Table  9. 

Of  the  72  averages  in  Barn  I,  30  were  below  1,000  bacteria  per 
cubic  centimeter  of  milk,  35  were  between  1,000  and  5,000,  only  7 
were  over  5,000,  and  of  these  seven  only  2  over  10,000.  In  Barn 
II,  30  of  the  47  averages  were  below  1,000,  and  the  highest  average 
was  only  3,599.  In  Barn  III,  all  the  averages  were  above  1,000  bac- 
teria per  cubic  centimeter  of  milk,  11  were  below  5,000,  6  were  be- 
tween 5,000  and  10,000,  and  2  were  over  10,000. 

As  in  the  germ  content  of  the  individual  samples  of  milk,  so  also 
in  the  average  germ  content  of  the  milk  of  the  different  animals,  a 
considerable  variation  took  place.  For  example,  in  Barn  I  Cow  174 
had  an  average  of  only  183  bacteria  per  cubic  centimeter,  while  Cow 
55  had  an  average  of  35,131.  In  Barn  II,  Cow  166  had  an  average  of 
149  bacteria,  while  Cow  550  averaged  3,599.  In  Barn  III,  Cows  1034 
and  1026  averaged  1,971  and  19,093  bacteria,  respectively.  It  is  also 


42 


BULLETIN  No.  199 


[May, 


of  interest  to  note  that  the  averages  of  the  cows  that  were  milked 
during  both  1914  and  1915  were  different  for  each  year.  In  some 
cases  the  difference  was  very  marked ;  for  example,  the  average  germ 
content  of  the  milk  from  Cow  167  was  444  bacteria  per  cubic  centimeter 
for  1914  and  6,092  for  1915,  and  the  milk  from  Cow  152  averaged 
1,044  and  12,168  bacteria,  respectively,  for  the  two  years. 

TABLE  9. — AVERAGE  GERM  CONTENT  OF  MILK  OF  INDIVIDUAL  Cows  FOR 
1914  AND  1915  RESPECTIVELY 

Barn  I 


Cow 
No. 

Average 
germ  content 
per  cc. 

Cow 
No. 

Average 
germ  content 
per  cc. 

Cow 
No. 

Average 
germ  content 
per  cc. 

1914  |   1915 

1914 

1915 

1914  |   1915 

26 
35 
55 
63 
73 
74 
110 
111 
112 
130 
134 
135 
150 
152 
154 

872 
723 
35131 
657 
927 
931 
665 
6835 
2010 
751 
1164 
325 
506 
1044 
1307 

1479 

155 
156 
167 
171 
172 
174 
176 
177 
178 
179 
180 
181 
182 
184 
186 

613 
763 

444 
602 
3874 
183 
826 
758 
925 
837 
2529 

408 
962 
6092 
2558 
4895 
1117 
2878 
4968 

187 
188 
189 
190 
191 
192 
193 
194 
195 
196 
198 
199 
200 
202 
203 

585 
5231 
387 
1140 
2213 
888 

1110 
718 
1440 
4899 
4571 
1476 
2955 
2816 
1998 
454 
1012 
3999 
1757 
3451 
1033 

26840 

1656 
986 
1679 

2185 
8250 
845 
870 
1019 
12168 

1088 
743 
2421 

833 
1391 
1042 

Barn  II 


Cow 
No. 

Average 
germ  content 
per  cc. 

Cow 
No. 

Average 
germ  content 
per  cc. 

Cow 
No. 

Average 
germ  content 
per  cc. 

1914 

1915 

1914 

1915 

1914 

1915 

108 
113 
116 
117 
118 
123 
125 
131 
137 
145 
149 

770 
636 
265 
1217 
2752 
329 
689 
1878 
1369 
657 
966 

159 
164 
165 
166 
170 
175 
183 
501 
550 
551 
552 

373 
813 
356 
295 
222 
2425 
1613 

311 

948 

553 
554 
555 
556 
557 
558 
559 
560 
561 
562 

1045 
1292 
3588 
1117 
603 

308 
189 
1766 
801 

149 
633 

1374 

"266 
555 
1789 
548 
1387 

1047 
236 
3599 
396 
212 

735 
1258 
635 

886 
901 



Barn  III 


Cow 
No. 

Average 
germ  content 
per  cc. 

Cow 
No. 

Average 
germ  content 
per  cc. 

Cow 
No. 

Average 
germ  content 
per  cc. 

1914 

1915 

1914  |   1915 

1914 

1915 

113 
137 
1003 
1015 

6991 
2124 

1018 
1019 
1025 
1026 

5324 
2748 
4320 
19092 

9342 
3759 

1031 
1032 
1033 
1034 

3150 
4603 
4598 
2667 

4010 
5086 
4834 
1971 

13120 
6414 

9178 

1917] 


GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  BARN  FACTORS 


43 


AVERAGE  GERM  CONTENT  OF  ALL  THE  MILK  AT  DIFFERENT 

MlLKINGS 

In  order  to  get  the  average  germ  content  of  all  the  milk  produced 
at  each  milking,  it  was  necessary  to  calculate  it  from  the  individual 
records,  since  all  samples  were  taken  from  the  milk  of  individual  cows 
and  not  from  mixed  milk  of  all  the  cows.  This  average  germ  content 
was  obtained^  therefore,  by  dividing  the  total  number  of  bacteria  in  all 
the  milk  produced  at  one  milking  by  the  total  number  of  cubic  centi- 
meters of  that  milk.  The  results  of  that  calculation  are  tabulated  in 
Tables  10  to  15. 

TABLE  10. — GERM  CONTENT  OP  TOTAL  DAILY  MILK  PRODUCTION: 
BARN  I,  1914 


Date 

Total  milk 
production 
in  cc. 

Total  germ 
content  of 
milk 

Average 
germ  content 
per  cc. 
of  milk 

Number 
of  cows 
milked 

March  ID  

143  023 

755  465  800 

5282 

26 

12  

70588 

127  812  050 

1810 

15 

13  

89312 

142  995  080 

1601 

16 

16  

111  596 

182  759  8,00 

1637 

19 

17  

205  919 

517  618  914 

2513 

38 

19  

199  449 

484  142  870 

2427 

36 

May   13  

111816 

106  981  000 

956 

20 

21  

118  673 

216  010  400 

1820 

21 

22  

121  002 

875  150  800 

7232 

21 

27  

126  189 

190  681  800 

1511 

21 

29  

129  177 

63  204  120 

489 

21 

June   1  

118  145 

109  030  430 

838 

20 

2  

118  848 

48  210  540 

405 

20 

3  

117  530 

79  945  420 

680 

20 

5  

54765 

39  311  100 

710 

10 

8  

99377 

1  043  284  410 

10498 

19 

9  

70368 

186  545  700 

2650 

-15 

10  

56567 

96  776  750 

1710 

12 

11  

104  430 

82  884  940 

793 

19 

12  

104  652 

208  767  710 

1994 

20 

13  

96532 

63  049  660 

653 

19 

15  

84196 

42  916  160 

509 

17 

16,  a.  m  

71335 

75  607  499 

1059 

15 

16,  p.  m.  .  . 

58237 

172  980  510 

2970 

15 

17,  a.  m  

65533 

40  232  670 

613 

14 

17,  p.m  

50  897 

52  797  540 

1037 

13 

18,  a.  m  

68  874 

69  369  560 

1007 

13 

18,  p.  m.  .  , 

55512 

84  315  960 

1519 

14 

19,  a.  m  

61973 

52  388  390 

845 

14 

19,  p.  m  

25  492 

16615430 

651 

8 

44 


BULLETIN  No.  199 


[May, 


TABLE  11. — GERM  CONTENT  OF  TOTAL  DAILY  MILK  PRODUCTION: 
BARN  I,  1915 


Date 

Total  milk 
production 
in  cc. 

Total  germ 
content  of 
milk 

Aver,  germ 
content  per 
cc.  of  milk 

Number 
of  cows 
milked 

March  10  

209  760 

703  593  000 

3  354 

33 

"  11  

238  450 

697  614  000 

2925 

37 

"  12  

228  920 

709  389  000 

3  105 

36 

"  13  

228  700 

722  367  000 

3  158 

36 

"  15  

233  200 

856  499  000 

3673 

35 

"  16  

243  760 

885  118  000 

3  630 

35 

"  17  

232  350 

892  646  000 

3  840 

34 

"  18  

245  750 

719  825  000 

2928 

35 

237  000 

736  142  000 

3  105 

35 

TABLE  12. — GERM  CONTENT  OP  TOTAL  DAILY  MILK  PRODUCTION: 
BARN  II,  1914 


Date 

Total  milk 
production 
ince. 

Total  germ 
content  of 
milk 

Aver,  germ 
content  per 
cc.  of  milk 

Number 
of  cows 
milked 

March 

23  

166  099 

146  887  500 

884 

26 

j  > 

25       

172  647 

96  287  000 

557 

25 

j  j 

26.  ..  :  

195  197 

202  127  100 

1  035 

25 

j  ) 

27  

168  340 

125  835  100 

747 

23 

)  > 

30  

195  943 

435  882  000 

2224 

23 

April 

2  

201217 

347  905  800 

1720 

23 

>  > 

3  

200  426 

45  504  300 

227 

23 

>  t 

6  

203  634 

95  930  600 

401 

23 

>  } 

8  

203  283 

55  541  600 

272 

23 

» 

9  

166  099 

63  860  400 

384 

23 

)  ) 

15  

201  745 

204  035  300 

1011 

23 

)  j 

18  

202  228 

189  717  900 

938 

23 

» 

22  

211  326 

225  902  200 

1  068 

23 

i  y 

24  

206976 

212  762  400 

1  027 

22 

>  > 

27.. 

200  558 

371  639  600 

1853 

21 

TABLE  13. — GERM  CONTENT  OF  TOTAL  DAILY  MILK  PRODUCTION: 
BAKN  II,  1915 


Date 

Total  milk 
production 
incc. 

Total  germ 
content  of 
milk 

Aver,  germ 
content  per 
cc.  of  milk 

Number 
of  cows 
milked 

March 

30  

171  250 

183  603  000 

1072 

21 

)  > 

31  

174  680 

103  339  000 

591 

21 

April 

1  

170  420 

74  382  000 

436 

21 

j  > 

2  

169  360 

340  440  000 

2010 

20 

)  > 

5  

167  670 

107  045  000 

638 

21 

>  > 

6  

170  720 

130  837  000 

766 

21 

» 

7  

172  660 

127  417  000 

737 

21 

t  j 

8  

172  140 

116  521  000 

676 

21 

it 

9  

172  480 

151  763  000 

879 

21 

>  ) 

12.. 

172  780 

87  308  000 

505 

21 

1917] 


GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  BARN  FACTORS 


45 


TABLE  14. — GERM  CONTENT  OF  TOTAL  DAILY  MILK  PRODUCTION  : 
BARN  III,  1914 


Date 

Total  milk 
production 
incc. 

Total  germ 
content  of 
milk 

Aver,  germ 
content  per 
ec.  of  milk 

Number 
of  cows 
milked 

April  15                        

73  929 

384  652  800 

5  203 

10 

»     18  

72566 

385  029  700 

5305 

10 

"     28  

54502 

502  218  700 

9214 

10 

»     30      

50854 

200  743  700 

3947 

10 

May      1  

60523 

252  388  900 

4180 

10 

"      2  

50  106 

340  778  300 

6801 

10 

"       4  

57974 

382  213  700 

6592 

10 

"       5         

53271 

238  415  500 

4475 

10 

"       6am       .    

55029 

244  532  300 

4443 

10 

"       6  p.  m  

48041 

317  808  600 

6615 

10 

"     11  

50  326 

361  966  203 

7  192 

9 

"     12  a.  m  

48  964 

282  436  100 

5  768 

9 

"     12  p.  m  

38  811 

589  285  700 

15  183 

9 

"     13  

50634 

199  918  900 

3948 

9 

"     14  

50898 

432  363  200 

8612 

9 

"     16  

48480 

200  273  700 

4131 

9 

"     18  .. 

48172 

336  195  700 

6979 

7 

TABLE  15. — GERM  CONTENT  OF  TOTAL  DAILY  MILK  PRODUCTION: 
BARN  III,  1915 


Date 

Total  milk 
production 
incc. 

Total  germ 
content  of 
milk 

Aver,  germ 
content  per 
cc.  of  milk 

Number 
of  cows 
milked 

March 

23  

49884 

291  376  000 

5842 

9 

>  ) 

24  

55298 

287  836  000 

5202 

8 

» 

26  

59025 

225417000 

3819 

8 

»  » 

27  

62855 

312  854  000 

4977 

8 

>  > 

29  

55525 

258  690  000 

4659 

8 

April 

1  

49713 

498  719  000 

10031 

8 

>  > 

2  

47  780 

129  098  000 

2  702 

g 

j  j 

5  

49010 

162  435  000 

3314 

7 

>  » 

7  

54110 

308  700  000 

5705 

8 

)  > 

21.. 

33625 

135  038  000 

4541 

5 

An  examination  of  Tables  10  to  15  shows  that  the  variation  in 
the  number  of  bacteria  in  the  milk  at  the  different  milkings  was  sur- 
prisingly small  in  each  barn. 

This  is  particularly  true  of  the  results  from  Barn  I  for  1915  and 
from  Barn  II  for  1914  and  1915.  The  lowest  average  daily  count  in 
Barn  I  during  1915  was  2,224  and  the  highest  count  was  3,840  bacteria 
per  cubic  centimeter.  In  Barn  II  for  1914  the  lowest  count  was  227 
and  the  highest  count  was  2,224,  and  for  1915  the  lowest  count  was 
436  and  the  highest  count  was  2,010  bacteria  per  cubic  centimeter. 

A  somewhat  more  pronounced  variation  in  the  average  daily  germ 
content  was  obtained  from  Barn  I  for  1914.  During  that  year,  how- 
ever, the  samples  at  that  barn  were  taken  from  only  a  part  of  the  herd 
and,  furthermore,  not  from  the  same  cows  at  each  milking,  and  it  is 


46  BULLETIN  No.  199  [May, 

probable  that  the  greater  variation  was  partly  due  to  this  procedure. 
It  is  of  interest  to  note  that  the  few  exceptionally  high  average 
daily  counts,  particularly  the  counts  of  May  22  and  June  8,  1914,  in 
Barn  I,  and  those  of  May  12,  1914,  and  April  1,  1915,  in  Barn  III, 
were  due  to  exceptionally  high  counts  in  the  milk  of  one  or  two  cows. 
For  example,  in  Barn  I,  on  June  8,  1914,  the  total  number  of  bacteria 
in  the  milk  of  the  19  cows  from  which  the  samples  were  taken  was 
1,043,284,410,  of  which  number  958,814,000  were  in  the  milk  of  Cow 
55  and  only  84,470,410  were  in  the  milk  of  the  remaining  18  cows.  If 
this  cow's  milk  had  been  excluded,  the  average  germ  content  of  the 
milk  of  the  remaining  18  cows  would  have  been  about  1,000  bacteria 
per  cubic  centimeter ;  but  with  the  milk  of  Cow  55  included,  the  germ 
content  was  10,498  bacteria  per  cubic  centimeter. 

COMPARISON  OF  THE  RESULTS  FOR  1914  AND  FOR  1915 

As  previously  noted,  in  1914  the  udders  of  all  the  cows  in  the  three 
barns  were  wiped  .with  a  damp  cloth  previous  to  each  milking,  but  in 
1915  this  practice  was  discontinued.  In  all  other  respects,  so  far  as  pos- 
sible, the  same  conditions  and  operations  were  maintained  during  both 
years.  However,  in  a  study  of  this  nature  certain  factors  which  may 
affect  the  germ  content  of  the  milk  are  often  beyond  the  control  of  the 
investigator.  For  example,  in  1914  the  study  extended  from  March 
10  to  June  20,  while  in  1915  it  was  necessary  to  confine  the  study  to 
March  and  April.  According  to  Stocking,  the  different  milkers  may 
decidedly  influence  the  germ  content  of  the  milk.  In  this  study  only 
two  of  the  sixteen  milkers  employed  in  the  three  barns  during  the  two 
years  remained  thruout  the  entire  period  of  the  experiment.  More- 
over, not  all  the  cows  milked  in  19]  4  were  milked  in  1915.  Some  of 
those  milked  in  1914  were  sold,  and  some  new  ones  were  added  during 
the  period  between  the  experiments  of  1914  and  1915.  Thus  71  cows 
were  milked  in  1914  and  67  in  1915,  and  only  49  of  these  were  milked 
during  both  years. 

The  difference  between  the  data  obtained  in  1914  and  in  1915  may 
be  emphasized  by  a  comparison  based  on  the  average  counts  of  the 
different  cows  grouped  as  shown  in  Table  16. 

It  is  seen  from  Table  16  that  there  was  no  appreciable  difference 
in  the  grouping  of  the  animals  in  Barn  II  and  Barn  III  for  the  two 
respective  years.  On  the  other  hand,  in  Barn  I  there  were  22  cows  in 
the  first  group  and  10  in  the  second  group  in  1914  and  only  8  cows  in 
the  first  group  and  25  cows  in  the  second  group  in  1915.  If  the  results 
are  expressed  in  percentage,  it  will  be  found  that  in  Barn  I,  62.9 
percent  of  the  35  cows  milked  in  1914  and  only  21.6  percent  of  the 
37  cows  milked  in  1915  were  in  the  first  group,  while  the  second  group 
contained  only  28.6  percent  of  the  cows  in  1914  and  67.6  percent  of 
the  cows  in  1915. 


1917] 


GERM  CONTENT  OP  MILK  AS  INFLUENCED  BY  BARN  FACTORS 


47 


TABLE  16.— COMPARISON  OF  EESULTS  IN  1914  AND  1915  BASED  ON  AVERAGE  GERM 
CONTENT  OF  MILK  OF  THE  INDIVIDUAL  Cows 


Number  of  cows  having  average  germ 
content  of  milk  — 

Below  1,000 
per  cc. 

Between  1,000 
and  5,00'0 
per  cc. 

Over  5,000 
per  cc. 

Bam  I: 
1914  

22 
8 

15 
15 

0 

0 

10 
.     25 

11 

6 

6 
5 

3 
4 

0 
0 

4 
4 

1915  

Barn  II: 
1914  

1915  

Barn  III: 
1914  

1915.. 

When  the  data  for  each  of  the  two  years  are  compared  on  the 
basis  of  the  average  germ  content,  per  cubic  centimeter,  of  all  the  milk 
produced  in  each  barn  during  the  entire  study,  the  relation  shown  in 
Table  17  is  obtained. 

TABLE  17. — COMPARISON  OF  RESULTS  OF  1914  AND  1915  BASED  ON  THE  AVERAGE 
GERM  CONTENT  OF  MILK  FOR  THE  THREE  BARNS 


Average  germ  content  per  cc.  of  milk 

1914 

1915 

Barn  I  

2140 
973 
6189 

3260 
830 
5050 

Barn  II  

Barn  III  

Average..                                                                 2188 

2552 

Table  17  shows  that  the  milk  produced  in  Barn  I  had  a  germ  con- 
tent of  1,120  bacteria  per  cubic  centimeter  less  in  1914  than  in  1915, 
while  the  milk  from  Barn  II  had  a  germ  content  in  1914  of  143  bacteria 
more  than  in  1915,  and  the  milk  from  Barn  III  had  a  germ  content  of 
1,139  more  in  1914  than  in  1915. 

The  data  for  the  two  years  may  also  be  compared  on  the  basis  of 
the  average  germ  content  of  all  the  milk  produced  in  all  three  barns  in 
1914  and  1915,  respectively.  Such  calculations  show  that  the  milk 
produced  in  1914  during  the  course  of  the  experiment  had  an  average 
germ  content  of  2,188  bacteria  per  cubic  centimeter  and  in  1915  an 
average  germ  content  of  2,552  bacteria  per  cubic  centimeter.  In  other 
words,  every  cubic  centimeter  of  milk  in  1914  contained  364  bacteria 
less  than  in  1915. 

In  all  three  barns  the  only  operation  that  was  intentionally  altered 
during  the  two  years  was  that  of  wiping  the  cow 's  udder  with  a  damp 
cloth  previous  to  each  milking.  The  data  for  the  two  years  show  that 
in  Barn  I  there  was  an  appreciable  increase  and  in  Barn  III  an  appre- 


48 


BULLETIN  No.  199 


[May, 


ciable  decrease  in  the  germ  content  of  the  milk  in  1915,  and  in  Barn 
II  the  germ  content  of  the  milk  was  approximately  the  same  for  both 
years.  It  is  evident  that  no  conclusion  can  be  drawn  from  the  data 
concerning  the  relative  importance  of  the  practice  of  wiping  the  ud- 
ders as  compared  with  the  other  sources  of  contamination  in  these 
barns.  The  data,  however,  do  point  to  the  conclusion  that  the  wiping 
of  the  udders  under  the  conditions  obtaining  in  these  barns  did  not 
affect  the  germ  content  of  the  milk  to  any  appreciable  extent. 

It  is  also  to  be  noted  that  .altho  pronounced  fluctuations  in  the 
numbers  of  bacteria  do  occur  in  the  individual  samples  and  in  the  aver- 
ages of  the  different  cows,  the  collective  influence  of  all  the  sources 
of  contamination  on  the  germ  content  of  the  total  daily  milk  production 
was  remarkably  uniform  for  both  years  in  each  of  the  three  barns. 


The  results  obtained  from  the  1,665  samples  of  milk  from  the 
three  barns  show  pronounced  variation.  Accordingly,  any  attempt  to 
estimate  the  combined  influence  of  the  various  sources  of  contamina- 
tion in  any  barn  on  the  basis  of  a  single  set  or  a  small  number  of  sets 
of  analyses  gives  no  dependable  results.  On  the  other  hand,  the  mass- 
ing of  the  results  from  a  large  number  of  samples  should  give  figures 
which  are  fairly  representative.  The  data  are  therefore  brought  to- 
gether in  Table  18  so  as  to  show  the  total  milk  production  in  each  barn 
during  the  study,  the  total  number  of  bacteria  in  the  milk,  and  the 
average  germ  content  per  cubic  centimeter  of  milk. 

TABLE  18. — GERM  CONTENT  OF  THE  TOTAL  MILK  PRODUCTION  FROM  EACH  BARN 


Total  milk 
production 
in  cc. 

Total  germ 
content  of 
milk 

Average  germ 
content  per 
cc.  of  milk 

Barn  I: 
1914                      

2  909  880 

6227838000 

2  140 

1915  

2  343  540 

7  640  708  000 

3260 

Total  

5  253  420 

13  868  546  000 

2639 

Barn  II: 
1914  

2  895  718 

2  819  813  000 

973 

1915  

1  714  160 

1  422  655  000 

830 

Total  

4  609  878 

4  242  468  000 

920 

Barn  III: 
1914     

913  080 

5  651  213  00-0 

6  189 

1915  

516  825 

2  610  163  000 

5050 

Total  

1  429  905 

8261376000 

5777 

1917]  GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  BARN  FACTORS  49 

According  to  these  calculations,  all  the  sources  of  contamination  in 
these  barns  contributed,  as  an  average  for  the  entire  investigation, 
2,639  bacteria  per  cubic  centimeter  to  the  milk  from  Barn  I,  920  bac- 
teria to  the  milk  from  Barn  II,  and  5,777  bacteria  to  the  milk  from 
Barn  III. 

The  purpose  of  this  investigation  was,  as  stated  before,  to  measure 
the  collective  influence  of  all  the  barn  factors  upon  the  germ  content 
of  the  milk,  and  not  to  measure  their  influences  separately.  Neverthe- 
less, the  data  obtained  point  to  certain  conclusions  concerning  the  rela- 
tive importance  of  some  of  the  separate  factors. 

The  influence  of  the  udder  of  a  given  cow  is  confined  to  her  own 
milk,  and  when  her  udder  is  a  large  factor,  numerically,  her  milk  will 
have  a  large  germ  content  regardless  of  the  degree  of  cleanliness  of 
the  barn  and  the  cow.  An  examination  of  Table  9,  page  42,  brings 
out  the  fact  that  the  number  of  bacteria  added  to  the  milk  by  the 
udder  was  small  in  the  case  of  most  of  the  animals.  In  Barns  I  and 
II,  61  cows  were  milked  in  1914  and  58  cows  in  1915.  The  average 
germ  content  of  60  of  these  119  cows  milked  during  the  two  years  was 
less  than  1,000  bacteria  per  cubic  centimeter,  and  of  32  cows  the  aver- 
age germ  content  was  between  1,000  and  2,000  bacteria.  It  is  evident, 
therefore,  that  since  the  small  average  counts  of  these  92  cows  were 
due  to  all  the  barn  factors,  their  udders  could  not  have  been  numeri- 
cally a  large  factor.  Of  the  remaining  27  cows,  20  had  average  counts 
between  2,000  and  5,000;  4  averaged  between  5,000  and  10,000;  one 
averaged  12,168 ;  and  one  had  an  average  of  35,131  for  1914  and  26,840 
for  1915.  In  the  case  of  the  last  animal,  Cow  55,  additional  study 
showed  that,  altho  apparently  healthy,  she  persistently  gave  milk  with 
a  high  germ  content,  the  source  of  which  was  her  udder. 

The  average  germ  content  of  the  milk  from  Barn  I  for  the  entire 
investigation  was  2,639  bacteria  per  cubic  centimeter.  If  Cow  55 
were  omitted  _from  the  calculations,  the  average  would  be  reduced 
approximately  1,000  bacteria  per  cubic  centimeter.  In  other  words, 
the  udder  of  Cow  55  alone  contributed  about  two-fifths  of  all  the  bac- 
teria that  were  found  in  all  the  milk  produced  in  Barn  I  during  the 
entire  investigation.  These  results  point  to  the  conclusion  that  in 
the  production  of  milk  of  low  germ  content,  the  udder  of  some  cows 
may  become  the  principal  source  of  contamination. 

This  conclusion  is  supported  by  the  studies  of  Hastings  and  Hoff- 
man and  of  Harding  and  "Wilson.  Hastings  and  Hoffman1  con- 
cluded that  "there  is  no  reason  to  believe  that  the  average  bacterial 
count  of  milk  as  it  is  drawn  from  the  udders  of  healthy  cows  is 
over  1,000  bacteria  per  cubic  centimeter."  These  authors,  however, 
found  that  the  milk  from  two  cows  in  the  herd  studied  averaged  30,700 
and  38,800  bacteria  per  cubic  centimeter,  respectively.  In  a  more 

'Hastings,  E.  G.,  and  Hoffman,  C.  Bacterial  Content  of  the  Milk  of  Individual 
Animals.  Wis.  Agr.  Exp.  Sta.  Ees.  Bui.  6,  pp.  189-196.  1907. 


50  BULLETIN  No.  199  [May, 

extensive  study,  Harding  and  Wilson1  examined  1,230  samples  of 
milk  taken  directly  from  the  udders  of  78  cows.  This  examination 
showed  that,  on  the  average,  only  428  bacteria  per  cubic  centimeter 
were  added  to  the  milk  by  the  udders  of  these  cows,  but  that  8  percent 
of  the  samples  contained  more  than  1,000  bacteria  per  cubic  centimeter, 
and  the  highest  count  was  16,610. 

The  2,639  bacteria  per  cubic  centimeter  in  the  milk  from  Barn  I 
may  be  considered  to  have  been  derived  from  three  separate  sources ; 
namely,  the  udder  of  Cow  55,  the  udders  of  the  remaining  cows,  and 
the  barn  factors.  Since  none  of  the  cows  in  Barn  II  gave  uniformly 
high  counts,  the  920  bacteria  per  cubic  centimeter  of  the  milk  from 
this  barn  may  be  considered  as  having  been  derived  from  two  sources — 
the  udders  of  the  cows  and  the  barn  factors.  If  it  is  assumed  that 
approximately  500.  bacteria  per  cubic  centimeter  were  added  by  the 
cow's  udders,  it  will  be  seen  that  the  conditions  and  operations  at 
Barn  I,  omitting  Cow  55  from  consideration,  contributed  approxi- 
mately 1,100  bacteria  per  cubic  centimeter  of  milk,  and  at  Barn  II 
about  400. 

The  general  appearances  of  Barns  I  and  II  would  seem  to  indi- 
cate that  Barn  I  was  the  cleaner ;  and  yet  from  the  above  deductions  it 
is  seen  that  more  bacteria  were  added  to  the  milk  at  Barn  I  than  at 
Bam  II.  It  might  be  argued  from  the  results  obtained  at  these  two 
barns  that  a  dirty  barn  does  not  contribute  more  bacteria  to  the  milk 
than  a  clean  barn.  Such  conclusion,  however,  would  be  against  a  well 
established  fact.  This  apparent  discrepancy  is  only  a  side  issue  to 
the  general  problem,  and  it  would  be  a  mere  conjecture  to  attempt  to 
explain  it.  The  real  significance  of  the  results  from  these  two  barns 
lies  in  the  fact  that  the  number  of  bacteria  in  the  milk  from  both 
barns  was  remarkably  small,  and  that  the  difference  in  the  conditions 
and  the  operations  in  the  two  barns  exerted  practically  negligible  in- 
fluence upon  the  germ  content  of  the  milk. 

Even  more  significant  are  the  results  from  Barn  III.  The  average 
contamination  here  was  5,777  bacteria  per  cubic  centimeter.  This  milk, 
so  far  as  the  germ  content  was  concerned,  would  meet  the  requirements 
for  certified  milk,  and  yet  the  conditions  of  the  barn  as  to  cleanliness 
were  such  that  it  is  doubtful  whether  the  milk  produced  here  would 
have  been  admitted  to  the  milk  supply  of  some  cities. 

These  results  must  not  be  construed  as  a  defense  of  dirty  barns. 
They  simply  point  to  the  fact  that  the  large  numbers  of  bacteria  com- 
monly found  in  milk  do  not  have  their  origin  in  the  barn. 


'Harding,  H.  A.,  and  Wilson,  J.  K.     A  Study  of  the  Udder  Flora  of  Cows. 
N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Tech.  Bui.  27.     1913. 


1917}  GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  BARN  FACTORS  51 


SUMMAEY 

This  study  was  conducted  in  three  dairy  barns,  differing  widely 
in  the  degree  of  cleanliness.  Samples  were  taken  from  the  milk  of 
individual  cows  when  the  milk  was  brought  from  the  barn  to  the  milk 
room  and  the  germ  content  of  each  sample  was  then  determined. 

A  total  of  1,665  samples  were  taken  from  138  cows.  The  samples 
were  collected  during  March,  April,  May,  and  June  in  1914  and  again 
during  March  and  April  in  1915. 

While  the  germ  content  of  the  individual  samples  varied  from  3 
to  218,250  bacteria  per  cubic  centimeter,  the  large  majority  of  the 
samples  in  all  three  barns  had  a  low  germ  content.  The  average  germ 
content  of  the  milk  of  individual  cows  was  low  in  most  cases.  Cow  55 
had  the  highest  average  of  35,131  bacteria  per  cubic  centimeter  of 
milk,  but  the  udder  of  this  animal  was  the  source  of  this  high  average. 
The  average  germ  content  of  all  the  milk  produced  at  each  milking 
was  over  10,000  only  once  in  Barn  I  and  only  twice  in  Barn  III,  and  in 
Barn  II  the  highest  average  was  only  2,224. 

The  milk  produced  in  1914  and  in  1915  had  approximately  the 
same  germ  content.  The  average  germ  content  of  all  the  milk  produced 
during  the  entire  study  was  2,639  bacteria  per  cubic  centimeter  in 
Barn  I,  920  in  Barn  II,  and  5,777  in  Barn  III. 


CONCLUSIONS 

The  study  of  these  three  barns  shows  that  even  under  wide  ex- 
tremes in  barn  conditions  it  is  possible  to  produce  milk  with  a  germ 
content  of  less  than  10,000  bacteria  per  cubic  centimeter  when  the 
utensils  are  properly  prepared. 

These  intensive  studies  made  at  the  Illinois  and  at  the  New  York 
Agricultural  Experiment  Stations,  together  with  accordant  observa- 
tions upon  about  twenty-five  ordinary  dairy  barns  by  the  former  insti- 
tution1 and  upon  thirty-four  dairy  barns  by  the  latter  institution,2 
make  it  plain  that  when  the  influence  of  utensils  is  excluded,  the  dairy 
barns  exert  little  measurable  influence  upon  the  germ  content  of  the 
milk. 


JIn  connection  with  other  studies  not  included  in  this  bulletin,  samples  of  milk 
from  about  one  hundred  different  barns  have  been  recently  examined  for  germ 
content,  and  in  no  case  did  the  varied  conditions  in  the  barn  have  any  marked 
effect  upon  the  germ  content  of  the  milk. 

"Brew,  James  D.  Milk  Quality  as  Determined  by  Present  Dairy  Score  Card. 
N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Bui.  398.  1915. 


Whenever  attempts  are  made  to  measure  barn  activities,  the 
attitude  of  the  workmen  becomes  an  important  element  in  the  success 
of  the  study.  Because  such  measurements  add  something  to  their 
labor,  the  men  may  become  antagonistic ;  or  because  such  measurements 
may  be  taken  as  an  index  of  the  care  with  which  they  do  their  work, 
they  may  modify  their  actions  during  such  tests  so  as  to  lead  to  ab- 
normal results.  Either  of  these  attitudes  may  modify  the  results  and 
endanger  the  conclusions.  Accordingly,  the  colleague  who  has  im- 
mediate charge  of  the  barn  workmen  becomes  a  vital  part  of  the  investi- 
gation and  his  influence  in  keeping  barn  conditions  normal  during 
the  progress  of  the  study  is  a  large  factor  in  the  success  of  the  work. 
Both  because  of  the  harmonious  relations  which  have  existed  and 
on  account  of  numerous  check  experiments,  we  believe  that  the  results 
here  given  are  representative  of  the  conditions  regularly  obtaining  in 
the  three  barns  in  which  this  investigation  was  made.  These  barns  were 
under  the  supervision  of  Professor  W.  J.  Fraser,  and  Messrs.  R.  S. 
Hulce  and  W.  T.  Crandall.  The  authors  are  greatly  indebted  to  these 
colleagues  for  their  hearty  cooperation,  without  which  the  investiga- 
tion could  not  have  been  performed  successfully, 


UNIVERSITY  OF  ILLINOIS-URBANA 


